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This aero package is an important aspect of setting up the
Ford GT to be fast that most don't pay enough attention too, I think this is
because the cars it runs with have much better down force and therefore people
don't think of the GT as a down force car. In the initial release notes of the
GT it made comment on the importance of creating a stable platform for
consistent down force.

A lot of the erratic handling people get can be from
inconsistent down force through a corner. For example if the front splitter is
very close to the ground under braking and initial turn in it can give very
good positive feel but if mid corner and tracking out the splitter lifts too
much you will lose front end grip. Even worse is on bumpy tracks the front is
too soft and the splitter bounces on the ground.

There is also down force generated through the rake of the
car and again having a stable platform is important to getting a consistent
feel / grip through a corner. Finally there is the rear wing which I use to
fine tune car balance in high speed corners.

Too many times I see sets trying to correct handling issues
by other means when in fact they are being caused by a poor aero platform.

My main goals when setting up the GT are:

1. Best possible aero
package I can get - most important when a track has a lot of medium to high
speed corners

2. Balanced handling
in all phases of each corner - i.e. oversteer or understeer do not dominate
in corner entry, mid corner and corner exit

3. Best possible
mechanical grip

Things that work for me in general are -

Aero Platform:

1. Running high ARB front and rear - most often at max 0 for
Qual and at 1 or 2 setting for Race and more often than not the front and rear
are at the same rate which is best for aero stability.

2. Run high rebound setting on front 36 to max 48 region
(mid to corner exit front end grip)

3. Set rake of car for track (anywhere from a few mm to
12-15mm depending on the track effects overall down force and car balance)

4. Pretty much always run with a low wing setting 3-6 degree
range

Overall Car balance:

1. Front / rear spring rate. Set front so that splitter
doesn't eat the pavement but as soft as possible then adjust the rear to get
the handling characteristic I need. Generally neutral to slight oversteer
tendency is what I'm after. Setting ARB to 2 or 3 when tunning spring rate will
enable you to read it better than ARB at either extreme.

2. Use hot tyre pressure to fine tune overall balance
(starting point is generally 2-3kPa lower at rear when hot)

3. A start point for the diff may be 70 power 55 coast and
4800Nm for preload with 4 plates (Preload can vary greatly depending on the
track some tracks a high preload works best 4800 to 5200 range others a more
moderate setting is best.)

Transient Car
Balance:

1. If car is balanced in slow to medium speed turns but
understeers or oversteers in high speed turns then rear wing and possibly rake
needs fine tuning.

Lower is not always better, consistency is better than
sporadic down force. I always like to see a small gap between tarmac and
splitter if it gets too low when it lifts you are going to get sudden changes
in front end grip = bad.

High rebound stiffness on the front is to
control the rate of rise of the splitter. If you can keep it down longer you
gain more down force induced front end grip. Remember set ups are often
compromises over several factors. Setting a car up for better aero is often
sacrificing ultimate mechanical grip if aero wasn't a factor.

• Tuning Suspension thoughts and ideas

Weight Transfer Dynamics

When discussing
transient response I always think of it in the weight transfer from one contact
patch to another.

A couple of things to remember in this regard are:

Shocks do not change the total amount of weight that will be transferred

Shocks only effect the rate at which weight is transferred (more resistance = faster transfer of weight)

Springs by themselves will not alter total load transfer but does change the rate at which it transfers (stiffer = faster)

Ride or roll centre height adjustment does effect total load transfer

ARB stiffness does not change how much total lateral load transfers but does effect the rate the load transfers

Generally more load transfer is a bad thing you want less transfer for higher grip for a tyre pair

Therefore it can be a bit of a trap to think of tunning
shocks in terms changing total load transfer between contact patches, you
should be adjusting ARBs, ride heights, aero, etc. for that purpose.

Shock bump and
rebound should first be tuned for best road holding ability of the tyres with a
given setup and then secondarily as a means of fine tuning transient response.

Load Transfer and Body Roll

If you reduce body roll by increasing ARB stiffness you
lessen the amount of body roll but do not change total lateral load transfer.

If you increase spring stiffness while keeping the centre of
gravity & roll centres the same you lessen the amount of body roll but do
not change total lateral load transfer.

If you lower the car and thus its centre of gravity / roll
centres you will then reduce body roll and lateral weight transfer.

All the above setup changes reduce body roll but have a
different effect on load transfer.

• Tuning the Diff

The Coast and Drive ramp angles for the Ford GT work the
same in that the lower the angle the more locking and the higher the angle the
less locking. What differs between Coast and Drive to the feel of the driver is
the effect it has.

Drive Angle

Higher drive ramp angle (e.g. 70-85deg) = lower locking on
throttle application, which allows the car to turn more readily when under the
limit of the tyres adhesion but if taken too far allows the inside wheel to
spin this can have the following symptoms: on slow speed corners loss of
traction and hence poor acceleration out of the corner, on high speed corners
it can result in understeer on mid corner and corner exit with throttle
application.

Lower drive ramp angle (e.g. 45-60 or lower) = more locking
on throttle application, which resists the car turning when under the limit of
the tyres adhesion but when approaching the limit of tyre adhesion allows the
driver to 'turn the car with the throttle". When taken too far it can
result in rapid throttle over steer. Lower drive ramp gives better acceleration
and enables the car to turn on medium to high speed corners easier without
having to lift off the throttle.

To set drive ramp angle I usually start with three plates
and 70deg, if the car is understeering on the mid to corner exits of high speed
corners or the inside wheel is spinning up under acceleration I will reduce the
ramp angle a click, if the car is entering throttle on oversteer to easily I
will increase the ramp angle a click.

Coast Angle

Higher coast ramp angle (e.g. 45-60 or higher) = lower
locking power under deceleration, this allows the car to turn more readily when
under the limit of the tyre adhesion but if taken to far allows a single rear
wheel lock up which can equal instability in the braking zone often ending in a
spin.

Lower coast ramp angle (e.g. 20-45) = more locking under
deceleration, which resists the car turning into a corner when under the limit
of the tyres adhesion. A lower coast ramp angle increases braking stability but
if pushed too hard can be unforgiving as both rear tyres will lose traction
together (not good).

To set the coast angle I usually start with 55deg, if the
car tends to lock up under braking I may reduce the angle a click or two.
Alternatively I would adjust brake bias forward.

Plates

On a side note on plates - my observation is that adding a
plate increases the locking factor by about the equivalent of 1.5 to 2 clicks
lower in ramp angle meaning 70 with 3 plates is approximately the same as 60-65
with two plates. With preload and plates I don't feel there is much difference
in preload when adjusting plates and therefore don't adjust preload if changing
amount of plates. Another interesting observation with number of plates is that
the less plates you have the diff reacts more quickly and aggressively, with
more plates the diff reacts a little slower and smoother.

Preload

Preload - preload is a tricky one to understand what is
best. Obviously higher preload means more locking when the car is neutral (i.e.
not accelerating nor decelerating). So the natural thought is that a higher
preload is bad as it resists turning mid corner right? So you should have it as
low as possible? There is much discussion about this even on real life forums
when it comes to building diffs, most diff builders will say as little as
possible is better. However there is evidence that some top level teams use
high preload in their diff builds and hence there is an alternative view that a
high preload diff is better. At the end of the day it will come down to driver
style and personal preference.

My preference is for higher preload and as such I start building
sets with a preload of 4800 kg and often use higher than that. The handling
characteristics that I am looking for in the GT with the diff are: strong
stability in the braking zone, a tight car that can be thrown into a corner
(understeery in neutral phase) and a car that can be steered with the throttle
mid corner to exit.

With that in mind my starting points for the diff in the GT
are Drive/Coast/Plates/Preload 70/5/4/4800 if the car is too loose mid corner I
will raise the preload if it is too tight I will reduce the preload. This
judgement is taken when in the scary mode when the tyre noise is telling you
that they are scrubbing, if you’re not judging it in that mode then you will be
adjusting it incorrectly.

One thing to note is that obviously preload has an interplay
with coast and drive locking and as such my starting points with building a
diff would likely be different with lower preload as a starting point. In other
words if you take a low preload diff setup for a given track and whack high preload
on it will likely not work nicely. If I change preload by a large margin I
normally also adjust drive and coast as well.